The present invention relates to footwear, particularly a cushioning member for a shoe sole. More particularly, the cushioning member is a fluid filled component having a plurality of support members configured to differentially collapse in response to a compressive load and provide improved shear compliance.
Considerable work has been done to improve the construction of cushioning members which utilize fluid filled bladders such as those used in shoe soles. Although with recent developments in materials and manufacturing methods, fluid filled bladders have greatly improved in versatility, there remain problems associated with obtaining optimum cushioning performance and durability.
One of the advantages of gas filled bladders is that gas as a cushioning compound is generally more energy efficient than open-cell foam typically used in athletic shoe soles. A typical open-celled foam used for midsole components is ethylene-vinyl acetate copolymer (EVA) foam. In many athletic shoes, the entire midsole is comprised of EVA.
Simple gas filled bladders have gas distributed generally within the bladder to provide a uniform cushioning response to a compressive load. Gas filled bladders are also generally moderated with foam to provide the necessary lateral stability to compressive loads applied obliquely as can happen in activities requiring a pushing off motion. In addition, simple gas filled bladders do not provide any means of adjusting or customizing the cushioning characteristics to obtain a softer or stiffer area where desired. Bladders can be formed and inflated so that discrete chambers are at different pressures. Such bladders are disclosed in U.S. Pat. No. 5,353,459 to Potter et al., which is hereby incorporated by reference.
U.S. Pat. No. 5,572,804 to Skaja et al., which is hereby incorporated by reference, discloses a shoe sole component comprising inwardly directed indentations in the top and bottom members of the sole components. Support members or inserts provide controlled collapsing of the material to create areas of cushioning and stability in the component. The inserts are configured to extend into the outwardly open surfaces of the indentations. The indentations can be formed in one or both of the top and bottom members. The indented portions are proximate to one another and can be engaged with one another in a fixed or non-fixed relation. In the Skaja patent, indentations are generally hemispherical in shape and symmetrical about a central orthogonal axis. The outside shape of the indentation, that is, the shape outlined at the surface of the bladder component is circular. The inserts have the same shape as the indentations.
The hemispherical indentations and mating support members or inserts responded to compression by collapsing symmetrically about a center point. While the hemispherical indentations and inserts of Skaja provide for some variation in cushioning characteristics by placement, size and material, there is no provision for biasing or controlling the compression or collapse in a desired direction upon loading.
U.S. Pat. No. 4,670,995 to Huang, which is hereby incorporated by reference, also discloses a shoe sole component comprised of inwardly directed indentations molded into flexible top and bottom sheets. The top and bottom sheets are joined at their outer peripheries, and the top and bottom indentations abut and are connected to one another, so that the top and bottom sheets are held in a spaced relationship and a sealed air cushion is formed. The abutting indentations provide a degree of vertical support and bend under increasing loads.
In addition, the sole of an athletic shoe is subject to very heavy intermittent compression loads and lateral stresses depending upon the activity for which the shoe is designed. For instance, court sports such as tennis and basketball entail quick, side to side movement, jumping and pushing off. The shoes designed for those sports must provide lateral support and have soles which are durable to oblique loads and their attendant shear stresses. For running sports, the shoes must also provide lateral support to prevent excessive pronation or supination, but are mostly subject to cyclic loading of the cushioning element typically beginning with initial lateral side footstrike followed by natural pronation and then supination to toe off. The cushioning element of a running shoe will also be subject to shear stresses in the lateral to medial direction as well as the toe to heel direction.
With hemispherically shaped indentations in the top and bottom of a shoe sole component, the indentations abut one another and are joined together by welding, adhesive or other means. The curved surfaces of the hemispherical indentations which adjoin another indentation are slightly flattened to provide a contact area. The contact area or weld is sized appropriately to the size of the indentations, and with hemispherical indentations, the welds are relatively small. As a result, the welds are a weak area of the sole component when subject to shear stresses, and improved shear stiffness in the sole is desired for durability.
The present invention pertains to footwear and to a bladder for a shoe sole with preferential collapse and recovery. The bladder of the present invention may be incorporated into a sole assembly of an article of footwear to provide cushioning. The bladder can contain fluid at atmospheric pressure, or can be pressurized. The bladder of the present invention provides for preferential collapse and selective cushioning by the shape and placement of indentations or carriers and mating inserts in the top and bottom surfaces.
The present invention overcomes the enumerated problems with the prior art, including a vulnerability to failure under shear loads.
In accordance with one aspect of the present invention, a bladder is formed of a barrier material with indentations in the top and/or bottom surfaces. When indentations are formed in both surfaces, the indentations abut one another and join one another in a contact area. At either the top or bottom surface of the bladder, the indentations have an ovoid shape, and are therefore asymmetrical about at least one axis.
At least some, and preferably each, of the indentations receive an insert having a corresponding shape. The insert is designed to collapse in response to a compressive load and then recover its shape. The profile of each insert and indentation pair is configured preferably as an ovoid, for preferential collapse in a predetermined direction. That is, the two ends of the ovoid have different stiffnesses to compression. One end collapses in response to a smaller compressive load than the other end. This results in a softer feel at one end compared to the other end. In this way, the insert and indentation can be positioned in a bladder to provide the most advantageous response characteristics.
The contact area or weld between abutting indentations is larger in surface area than the welds between the prior art hemispherical indentations. In the present invention, the welds are shaped to correspond to the shape of the inserts which contributes to stability and are more resistant to oblique and eccentric loading which exert shear forces on the welds.
The bladder is constructed of barrier materials and shaped appropriately for placement in a shoe sole component. The bladder has a number of abutting indentations for receiving inserts. The insert and indentation combinations are disposed in the bladder so as to provide a desired pattern of cushioning and support in response to anticipated compressive loads. The pattern will vary depending upon the activity for which the shoe sole is designed.
Footwear, according to the present invention, can incorporate the bladder in any position along the length of the sole, and the preferential collapse of the indentations and inserts are arranged to take into account the foot motions that typically occur at that location of the sole in the type of activity for which the footwear is designed. In an illustrated example, the bladder is located in the heel of the sole and the indentations and inserts are arranged to account for lateral heel strike and pronation of the heel during running.